Depending on the timeframe you come down, there's a place on the east coast off Palm Beach that Lemon Sharks frequent. I've been on a dive with them, and it is an awe inspiring event.
The following quote is copied from Jim Abernathy's Scuba Adventures Page at
http://www.scuba-adventures.com/sharks.shtml. I'm not associated with them in any way whatsoever, other than I have used them in the past for dive charters.
"In Palm Beach , we see these solitary animals occasionally on deeper reefs, but recent findings have shown a migration of sorts in northern Palm Beach County in numbers up to 50+. In January and February, when the water is colder, in the low 70's, they have been seen lying in the sand very close together. Scientists are still trying to figure out exactly what they are doing there. It is most likely courting or mating related. It is however a very unique and amazing spectacle. Until 2000 it had never been heard of anywhere in the world. Scientist are now trying to get this particular area zoned "off limits" to fishing and especially lemon shark fishing during this aggregation and protect the migrating sharks who come here as they most likely make up a large population of lemon sharks on the east coast. Depending on how large the aggregarion is, we will run special trips to see them. FYI - Lemon sharks get their name from their light coloration. Males seem to be thinner than the females who can reach over 10 feet in length and be very bulky. They have a pointy snout and small eyes as well as two dorsal fins, like a nurse or sand tiger shark. "
If you're interested in seeing a shark or two, this would be an opportunity to see a "Nice" shark.
This is my $.02 on it. Other than that, I'm all over some more diving over in Venice. Like the others stated, post it up a little in advance of your trip, and I'm sure you won't have any problem finding a guide or a buddy.